1. Field of the Invention
The present invention relates to a monitoring switching method and apparatus for an apparatus that is redundantly configured in part and, more particularly, to a method and apparatus for fault monitoring and switching control for a redundant part of a transmission apparatus used in digital communications.
2. Description of the Related Art
FIG. 1 shows an example of fault monitoring and switching control for a duplexed part of a transmission apparatus some of whose constituent units are arranged in a duplexed configuration.
In FIG. 1, reference numerals 1-1 and 1-2 are duplexed information transmitting units having pattern insertion circuits 1-4 and 1-5, respectively, for performing path monitoring within the apparatus. The block indicated at 1-3 is also an information transmitting unit, which comprises a circuit 1-6 for monitoring a pattern from the unit 1-1, a circuit 1-7 for monitoring a pattern from the unit 1-2, and a selector (SEL) circuit 1-8 for selecting one of the units 1-1 and 1-2. Reference numeral 1-9 is a monitoring control section for providing signal restoration by controlling the SEL circuit 1-8 in the event of a fault based on the pattern monitoring outputs of the circuits 1-6 and 1-7. That is, when a fault is detected by the circuit 1-6, the SEL circuit 1-8 is controlled to switch the channel from the unit 1-1 to the unit 1-2, and when a fault is detected by the circuit 1-7, switching is made from the unit 1-2 to the unit 1-1.
FIG. 2 is a diagram for explaining a fault evaluation method for identifying a faulty unit based on a detected fault, and a switching method for switching the duplexed units, in a configuration where the transmission apparatus is implemented by combining multiples of the configuration shown in FIG. 1.
In FIG. 2, similarly to the first described configuration, reference numerals 2-1 to 2-5 are information transmitting units, 2-6 to 2-9 are pattern insertion circuits, 2-10 to 2-15 are pattern monitoring circuits, 2-16 to 2-18 are SEL circuits each for selecting one of its upstream units, and 2-19 is a monitoring control section for monitoring patterns and controlling the SEL circuits.
As an example, when a fault is detected by the pattern monitoring circuit 2-10, the fault evaluation and switching control has been accomplished in one of the following two ways.
(i) Assuming that the unit 2-1 has failed, the SEL circuit 2-16 in the unit 2-3 is controlled to switch out the unit 2-1. (The most suspect unit is determined to be the faulty unit).
(ii) Assuming that the units 2-1 and 2-3 have both failed, the SEL circuits 2-16 and 2-17 in the units 2-3 and 2-4 are controlled to switch out the unit 2-1, and further, the SEL circuit 2-18 in the unit 2-5 is controlled to switch out the unit 2-3. (All suspect units are determined to be faulty).
In the method of FIG. 1, since the pattern monitoring circuits 1-6 and 1-7 can fail themselves, such failures must be distinguished in order to accurately identify the faulty unit. This necessarily increases the complexity of the fault detection mechanism of the pattern monitoring circuits.
Furthermore, since the pattern monitoring circuits 1-6 and 1-7 are placed in front of the SEL circuit 1-8, there is an unmonitored section including the SEL circuit 1-8 itself. To solve this problem, a pattern monitoring circuit must be added after the SEL circuit 1-8, which further increases the complexity.
On the other hand, the methods of FIG. 2 involve the following problems.
With the method (i), when the unit 2-1 is not faulty but the unit 2-3 is faulty, the transmission line cannot be restored.
With the method (ii), since the units 2-1 and 2-3 are both determined to be faulty, unnecessary switching occurs when only the unit 2-3 is faulty.
It is accordingly an object of the present invention to provide a monitoring switching method and apparatus that can, with simple circuitry, accurately identify and switch out a faulty unit.
According to the present invention, there is provided a monitoring switching method for a redundant part of a transmission apparatus, comprising the steps of: in a plurality of redundantly configured units, inserting respectively different signal patterns in respectively different time slots for signals passing through the respective units; controlling a selector to select all of the inserted signal patterns in sequence, the selector being configured to accept outputs from the plurality of redundantly configured units and to select from among the outputs one main signal for output; monitoring the signal patterns at an output side of the selector; and controlling the selector based on the result of the monitoring.
According to the present invention, there is also provided a monitoring switching method further comprising the steps of: in a plurality of second redundantly configured units each having the selector, inserting respectively different second signal patterns in respectively different time slots for signals passing therethrough; controlling a second selector to select all of the inserted second signal patterns in sequence, the second selector being configured to accept outputs from the plurality of second redundantly configured units and to select from among the outputs one main signal for output; monitoring the second signal patterns at an output side of the second selector; and controlling the selector and the second selector based on the results of the monitoring of the signal patterns and the second signal patterns.
According to the present invention, there is provided a monitoring switching apparatus for a redundant part of a transmission apparatus, comprising: a plurality of pattern inserting sections, respectively provided in a plurality of redundantly configured units, for inserting respectively different signal patterns in respectively different time slots for signals passing through the respective units; a selector for accepting outputs from the plurality of redundantly configured units, and for selecting from among the outputs one main signal for output and also selecting all of the inserted signal patterns in sequence; a pattern monitoring section, provided on an output side of the selector, for monitoring the signal patterns inserted by the pattern inserting sections; and a monitoring control section for controlling the selector based on the result of the monitoring performed by the pattern monitoring section.
According to the present invention, there is also provided a monitoring switching apparatus further comprising: a plurality of second pattern inserting sections, respectively provided in a plurality of second redundantly configured units each having the selector, for inserting respectively different second signal patterns in respectively different time slots for signals passed through the pattern monitoring section; a second selector for accepting outputs from the plurality of second redundantly configured units, and for selecting from among the outputs one main signal for output and also selecting all of the inserted second signal patterns in sequence; and a second pattern monitoring section, provided on an output side of the second selector, for monitoring the second signal patterns inserted by the second pattern inserting sections, and wherein the monitoring control section controls the selector and the second selector based on the results of the monitoring performed by the pattern monitoring section and the second pattern monitoring section.